In situ electrolinking of oil shale



June 16, 1964 H. w. PARKER 3,137,347

IN SITU ELECTROLINKING OF OIL SHALE Filed May 9, 1960 2 Sheets-Sheet l PRODUCTS 26 OVERBURDEN OIL SHALE FIG. 2

PRODUCED GAS &OIL

OVERBURDEN OIL SHALE HIGH RESISTANCE SECTION INVENTOR. H. W. PARKER F/G. Mfg:

A 7' TORNEYS Jun 16, 1964 H. w. PARKER 3,137,347

IN SITU ELECTROLINKING OF OIL SHALE Filed may 9, 1960 2 Sheets-Sheet 2 FIG. 3

INVENTOR. H. W. PARKER BY 2 i A TTORNEVS United States Patent 3,137,347 1N SITU ELECTROLINKING OF OIL SHALE Harry W. Parker, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed May 9, '1960, Ser. No. 27,627 5 Claims. (Cl. 166-39) This invention relates to an improved method for producing hydrocarbons from oil shale by heating the oil shale by electrical resistance.

Electrolinking refers to the passage of an electric current through a hydrocarbon-containing formation with a suflicient current density to create low resistance paths through the formation. This concept is disclosed in a patent issued to Erich Sarapuu, US. 2,795,279, Method of Underground Electrolinking and Electrocarbonization of Mineral Fuels. This patent states that a definite value of electrical resistance is required in the original formation.

Oil shale differs from other hydrocarbon-containing subterranean deposits in that it is usually dry and is not electrically conductive and therefore not amenable in its natural state or condition to electrolinking. oil-bearing strata contain connate water including dissolved salts which permit passage of electric current thru the same at sufiicient rate to heat and retort the strata. Even coal seams contain sufficient moisture to permit electrolinking.

Electro-carbonization tests were applied to samples of tar sands from Iantha and Deerfield sites of Missouri.

and were visibly unaffected by the treatment even I at 14,000 volts. Y

The maximum voltage was applied without effect across one sample of about 1% inches in length. This was the shortest sample used, and the resulting macroscopic voltage gradient amounted to about 500 volts per millimeter.

In those cases in which breakdown was accomplished the gross voltage gradient was less than this value. Tests on a sample of tar extracted from a sample from the Deerfield site indicated that the breakdown strength of the pure tar was of the order of 6000 volts per millimeter.

' of tar Were subjected to voltages up to 14,000 volts and process.

Other The samples were placed between electrodes having a parable in size to the perm plugs, and (c) three largev irregularly shaped blocks about 6 inches by 10 inches and three to six inches thick. In those cases, in which a breakdown of the sample was accomplished, the sample was further heated by applying 1000 to 2000 volts at 15 milliamperes.

The sequence of events, in those cases in which the sample was successfully electro-carbonized, was in general as follows:

(1) Voltage, 05000 volts; current rises approximately in accordance with Ohms law as the voltage increases. A frying, or spluttering, sound is produced, and considerable sparking takes place over the surface of the sample.

(2) Voltages, 5000l0,000 volts; both current and voltage fluctuate as the electrical activity over the surface of the sample increases. Current may increase without a corresponding increase in voltage. Some heating takes place. vj

(3) The current suddenly increases to very large values as the voltage falls to a .value between 2000 and 5000 volts. Violent heating occurs With the production of much smoke, and the tar melts and boils out of'the core.

(4) If the heating is prolonged, the smoke eventually disappears and the core takes on ,a coke-like appearance. The current remains high voltage. V

Some of the samples failed to respond at all to this treatment. That is, voltages up to 14,000 volts were applied withno apparent effect on the sample. The curand relatively independent of rent through the sample remained zero at this'voltage.

to temperatures up to 120 C. This application of heat did not appear to facilitate in any way the carbonization Such behavior would lead one to conclude that electro-carbonization is accomplished by high localized potential gradients induced by breaking current paths in the water phase rather than by gross potential gradients in excess of the breakdown gradient of the tars. a

On the basis of these results, therefore, one must conclude that two conditions are necessary for the successful electro-carbonization of a hydrocarbon bearing rock.

(1) A continuous hydrocarbon phase: That is, sufthe heated shale becomes electrically conductive. This was demonstrated by placing two copper electrodes between sections of Colorado oil shale. The electrodes were about one-half inch apart and the space between them was filled with a graphite powder and brine paste. When about 13 volts was appliedto these electrodes, approximately 100'watts of powerwas dissipated. In five minutes the shale adjacent the electrodes burst into flame and this was-followed by cracks in the shale. The heating was allowed to continue for 15 minutes before the power was shutoff.

When cool it was found adhered to each other. When one block was removed the heat affected zone broke away. The electrical resistance of this affected zone Was'estimated by placing Ohm meter'probes approximately /8 inch aparton its surface. The measured resistance was about 300 ohms.-

It has been found that oil shaleheated to elevated temperatures by any'heat source lowers the electrical resistivity thereof and renders the same sufliciently; conductive to permit producing the shale by electrical resistance heating. Oil; shale samples, bothj'raw andfrd 'torted, were subjected to electrical resistivity tests at various temperatures. The data obtained are set forth below.

- Tempera-- :Re'sistivity Sample ture, (Ohm- I F. cm.)

. Raw shale H .70 5.1X10 Retorted shal'e... 5, 500 'Do V 700 -i 700 uniform .tar distribution couldn'ot be electrocarbonized that the shale blocks hada It isan object of the invention to provide an improved process for producing oil shale by electrical re-' sistance heating with current passing thru the shale. A further object is to provide an improved process for the in situ production of oil shale utilizing electrical conductive media around and between electrodes utilized in heating the shale by electrical resistance of the shale. A further object is to provide a means of heating shale between electrodes within a single well by electrical resistance of the shale. It is also an object of the invention to provide a process for producing oil shale between directionally drilled wells by electrical resistance heating of the shale. Other objects of the invention will become apparent upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises preheating dry oil shale, which is substantially a non-conductor of electric current at normal temperatures, to an elevated temperature so as to render the shale sufficiently electrically conductive to permit further heating by electrical resistance heating; passing current thru the hot shale so as to further heat and retort the shale, thereby driving therefrom valuable hydrocarbons; and recovering the hydrocarbons thus driven out. The oil shale is heated by an electric heater in contact with or close to the shale, by flowing hot gas thru the shale, or by a downhole gas fired heater, etc. The resistance heating system may be energized during the preheating step, in the later phase thereof, or after the temperature of the shale between the heating electrodes has been raised to 400 F. and, preferably, .to700F.

One embodiment of the invention comprises providing an electrical conductor cable extending from ground surface into an oil shale stratum within a borehole there- .in, packing said borehole around the cable with a particulate electrical conductive material in close contact with the shale and in contact with said cable as a first electrode, providing a second electrode in the shale, passing electric current between said electrodes thru said conductive material, so as to heat adjacent shale and distill hydrocarbons therefrom and render same conductive, and recovering produced hydrocarbons from a borehole in the shale communicating with the heated area. are positioned one at an upper level of the shale and the other at a lower level of the shale so that the current passes thru the conductive material packed in the well between the electrodes. The electrode at the bottom of the well is axially positioned and extends from a conductive material at the bottom of the Well to ground level, being insulated from the surrounding conductive material except at its lower end, as by a surrounding conduit from which it is insulated. V j f In a further embodiment, two wells are directionally drilled from spaced apart points at ground level so that In one embodiment of the invention, the electrodes their lower ends are in close proximity to each other.

The oil shale between the ends of thewells-is fractured and the connecting fracture is filled with a conductive material. Conductive cable is provided in each well leading to the conductive fracture and the cables within the stratum are surrounded by conductiveparticulate solid material.

be had by reference to the accompanying schematic drawing of which FIGURE 1 is an elevation thru a well in.

an oil shale stratum with equipment for producing the shale by resistance heating; FIGURE 2 is a view similar In a further embodiment a well is drilled to penetrate the shale intermediate the ends of the di-' 4 thru a test apparatus used in producing a block of oil shale. V l

Referring to FIGURE 1, an oil shale 10 is penetrated by a borehole llwhich is provided with a casing 14 extending into the upper level of the shale.

and is surrounded within the oil shale by a packed bed of solid particulate conductive material 18. Tubingsec tion 19 within the packing 18 is constructed offnonconducting material such as ceramic, plastic, or the like.

An electric cable 20, insulated from well tubing 16,Iex tends thru the tubing to a conductive plate 22 which serves as the lower electrode in the system. Cable 20 comprises a wire conductor encased in magnesia withinan armored sheath, the armored sheath being removed from the lower end section of the cable. Casing 14 is connected to a power source (not shown) by conductor 24 and serves as the upper electrode. The power source is also connected by conductor 26 with cable 20.

In order to render the arrangement more effective in establishing resistance heating in the oil shale, a layer or section of relatively high resistance material 28 is positioned intermediate electrodes 14 and 22, preferably mid-way, so that during the heating of the shale adjacent the packing this layer overheats and melts the conductive material therein to retard or cut off the flow of current therethru.

the layer or section 28. This is now possible'because' of the increase in temperature of the shale which'renderls it conductive. produced area around well 12.

In FIGURE 2, directionally drilled wells as and 32" penetrate oil shale 10 and the bottom ends approach each other in the lower section of the shale. The. intervening shale is fractured by conventional means to produce fracture 34. This fracture may be effected by pressurizing either well 30 or 32 with fracturing fluid prior to drilling production well 36; or the fracture may be made thru Well 36 in conventional manner. Well '36 is provided with casing 38 and with product take-off line 40. A line 42 leading into the casing is also pro- Wells 30 and 32 may also be cased to any suitable depth asto vided for injecting air, steam, and other gases.

the upper level of oil shale 10.

In FIGURE 3, a cylindrical plug of dry Colorado oil V shale 44,5 /2 high, 6% in diameter, and weighing 7.33 kg. .is insulated at the top and bottom with asbestos paper 46 and 48, respectively, of a thickness ofJA.

The block of shale was enclosed by means of circular steel flanges '50 held by bolts 52 and by a cylindrical sheet were inserted in hole 56 about 5 /3 of the way thru the block of shale to extend 1%" into the same, leaving a space of 2" between their inner ends. That portion of the stainless steel tubes within the block of shale was encased in an annulus 62 of --20 mesh iron filings. +10

3 weight percent CuSO -5H O and wet with water after to FIGURE 1, showing a pair of directionally drilled wells with an intervening fracture and an intermediate packing. This moist paste provided close contact with the shale and the tubes. Thermocouples 64 were positioned inside the stainless steel tubes within thedevice and connected with leads to recording apparatus not shown. A fluid take-ofi line 65 was provided to recover fluids produced "at the periphery of-the shale. The entire device was covered with 2' of glass wool. A line (not I shown) was connected with the interior of tubes 62 to recover internally produced fluids.

The block of shale in thedevice of FIGURE 3was subjected to the following tests: Y

:(I) At room temperaturev when electrodes 58 and 60: were energized (250 v.) the resistance wasso high that A well tubing 16 extends thru the well head to the bottom of the well,

This has the eifect of forcing the current to pass thru the heated'shale adjacent the well and opposite Dotted lines 29 indicate the heated and substantially no current flowed. For two hours a diameter quartz heater with a ,6 heated length was placed in hole 56. During' the second hour of heating, 250 volts A.C. was applied to the electrodes. No significant amount of current flowed between the electrodes until 1.3 hours passed. From 50 to 100 Watts was applied to the quartz heater and temperature inside the electrodes reached 1300 F. at times. At the end of two hours,.there was sufficient resistance heating within the shale to dispense with the quartz heater and it was removed. All further heating was applied by electrical conduction thru the shale.

(II) For 4.4 more hours (6.4 total), a power input of 100 watts was maintained and the interior temperature of the electrodes was maintained below 900 F. during this time. The resistance between the electrodes had decreased to 3.3 ohms at this time. Oil production to this point was only 0.5 cc., surface temperature of the shale was 400 F.; hence, it would be assumed that oil was condensing in the fractured shale.

(III) Power level was now increased to 200 watts over a period of 1.9 hours (8.3 hours total). This power level was held for 5.1 hours (13.4 hours total). Total oil production to the end of a 12.3 hour period was 44 cc. The average oil production rate from 10.3 to 12.3 hours was 17.5 cc./hr.

(IV) Resistance between the electrodes decreased to 0.194 ohm at the end of 12.3 hours. In order to demonstrate the concept of injecting air or steam to remove carbon from the spent shale and thus increase the flow of current thru the shale being retorted, about 100 cc. per minute of air (70 F. and 15 p.s.i.a.) was injected thru one of the electrodes. The air injection was continued for 1.1 hours at which time the resistance between electrodes had increased to 1.1 ohms.

Total oil production at the end of 13.4 hours was 75 cc., indicating a rate of 28.2 cc./hr. (V) The input power at the end of 13.4 hours was gradually decreased from 200 watts to 130 watts to maintain the measured interior temperature below 1000" F. The injection of air was being continued. 'Prior to air injection, the maximum temperature was 1300 F. Oil production by the end of 15.0 hours was 138 cc. which indicates a rate of 39 cc./ hr. This increased oil production rate with decreased interior temperature and power input indicates improved use of the applied powerdue to air injection.

(VI) At the end of 15.5 hours, a gas sample was taken,

gas being produced at the rate of 7.7 cc./sec. (corrected to 760mm. O.C.)..

The analysis is given in the table below. Power input was still 130 watts. (Much of'this power was being lost due to the high heat loss system in which the test was being made.) Total oil production at the end of 16.2 hours was 186 cc., indicating a rate of 37.5 cc./hr.

(VII) The run was terminated by choice of the operator at the end of 16.5 hours. At thistime the system was operating satisfactorily and oil production was stable. The total oil production was 202 cc.

The oil production of the runs had the following properties:

Oil Properties The injection of air and/ or steam, as described in step (IV) was effected while current was flowing thru the shale. It is also feasible to cut oil the flow of current while the airand/or steam is being injected toobtain improved results.

In utilizing an arrangement shown in FIGURE 1, current is caused to flow thru the fluid permeable conducting material 18, packed in the wellbore, between electrodes 14 and 22. In this manner, the shale adjacent the well is heated by conduction and radiation sufiiciently to become electrically conductive. Current then flows thru the shale and thus heats additional adjacent raw shale. By this means the current conducting zone expands about the well as indicated by lines 29. In order to encourage the flow of current thru the shale, it is desirable toinclude in the packing material 18 the high resistance section 28 which fails as a conductor when the temperature thru the high resistance section becomes excessive. This high resistance section may comprise one or more layers of non-conducting alumina, glass, or

ceramic pieces, preferably in the form of pebbles or balls,

with the particulate conducting material 18 occupying the interstices or voids between the pebbles. As the temperature increases with current flow, the highest temperature in the system develops at the high resistance section and this section can be made to fail after heating up the adjacent wall of the borehole by suitably increasing the flow of current until this occurs. Thereafter, the current, at least the shalel Conducting medium 18 has been made from iron filings over which copper sulfate solution has been flushed and, also, from steel wool wet with graphite-brine paste, and these havebeen successfully utilized in laboratory tests. In field operation, metal and/or graphite frag ments are useful as packing material. It is necessary for the well bore packing to have sufficient permeability to In order toprevent allow produced gasesto escape. damage to. the insulated electrode at the axis of the wellbore, the packing material can'be made from a metal or other conducting material with a relatively low melting point so that the packing would melt before damage to the electrode could occur. Zinc and copper are metals which would function in this manner, assuming that the axial insulated cable in the well bore has a conductor of iron, Nichrome, or other metal melting at a higher temperature than copper or zinc. After shale adjacent the well has been heated sufliciently to become retorted, horizontal fractures develop along the bedding planes and thus force a greater portion of the current to flow adjacent raw shale. The swelling shale prior to being retorted maintains firm electrical contact in the heated but not fully retorted oil shale. These two factors permit the conducting zone to move a substantial distance into the formation.

The rate of current flow controls the temperature in the well. This temperature is regulated to prevent damage to the electrodes in the well; The temperature is also controlled to prevent decomposition of carbonates and,

greater part of it, must flow thru the will vary, depending upon the conductivity of the material packed in the well bore. When the heated zone has proceeded an appreciable distance into the formation the resistivity of heated shale determines the voltage requirements. Electrical apparatus similar to that used by the Bureau of Mines for electrolinkingcoal is satisfactory. (Bureau of Mines Report of Investigations 5367, Field-Scale Experiments in Underground Gasification of Coal at Gorgas, Ala., October 1957, pages 14 to 32.)

The cost of electrical power would be a major item in the operation of this process. Electric heaters placed in wells have been previously employed to retort shale commercially in cases where economical hydroelectric power was available. is superior to simple well heaters in that the source of heat is adjacent the shale being retorted and thus the rate of heat transfer is not limited. Since this process produces fuel gas the cost of electricity would be due to plant investment and maintenance and not to fuel costs.

After the electrically conductive zone has been established in the shale, as described above, it is extended indefinitely by drilling additional wells into the conducting shale andpacking them with a conducting material.

Power is then supplied to these Wells to cause the conducting zone in the shale to advance. These wells might be directionally drilled so that a greater spacing could be employed. Adjacent wells may be fractured into the conducting zone with an electrically conductive material to provide a path for current flow.

After a large volume of shale has been retorted in this manner air and/or steam may be injected into the spent shale to make fuel gas fro mthe coke remaining on the spent shale. The removal of coke by air and/ or steam would also prevent current flow through spent shale.

This invention applies to production of oil shale in multiple well systems by resistance'heating of the shale. When only one well is used for the process,it is necessary to provide a path for current to flowup the Well by means of an insulated electrode. This electrode must be protected from excessive temperatures. The electrode may be avoided by use of a multiple well system. The wells may be linked together by either fracturing or directional drilling. A combination of directional drilling and fracturing may prove most useful as shown 7 in FIGURE 2. With this method directional drilling need not be depended upon to directly hit another well. Also, in this combined technique the conductivity of the material in the fracture need not be as large, nor as reliable as'it would be in the case offracturing alone.

This technique is illustrated in FIGURE 2. The well in the center provides for the production of oil and gas The resistance heating technique which could be electrolinked as well as conducting solids .Mines R1. 3779, Horizontal Drilling for Oil in Pennsyl- Vania) Horizontal drilling would allow production of so that the current-carrying wells need not also produce gases. If desired, one'well of the three illustrated could be eliminated and the products produced through a current carrying well. The wells could be packed with solids .a selected shale stratum and thus concentrate the electrical power in the most productive zones.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative de-. tails disclosed are not to be construed as imposing unnecessary limitations on the invention. a

I claim:

1. A process for producing hydrocarbons from oil shale in situ which comprises providing an electrical conductor cable, fully insulated except a lower end section thereof'and extending from ground surface into a lower level of said shale within a borehole; packing said bore hole around said cable solely within said shale with a particulate electrical conductive material in close contact .With said shale and in contact with the lower uninsulated end of said cable as a first electrode; providing a casing extending into the upper section of said conductive material as a second electrode in said shale; passing electric current between said electrodes thru said conductive material so as to heat adjacent shale and render same conductive and distill hydrocarbons therefrom; and recovering produced hydrocarbons from a borehole in said shale communicating with theheated area.

2. The process of claim 1 wherein a transversesection of high electrical resistance is positioned across said borehole intermediate saidelectrodes so that same heats more than the remaining conductive material upon continued flow of current and melts, thereby forcing current to flow thru the adjacent shale to bypass said section. a

and distilling hole.

3. The process of claim 2 wherein said section of high electrical resistance is formed of a layer of particulate inhydrocarbons more remote from said bore sulating material interspersed with said conductive material.

4. The process of claim 1 wherein said conductive ma terial comprises a graphite-brine paste.

5. The process of claim 1 wherein said conductive 0' material comprises iron Wet with copper sulfate solution.

References Cited in the file of this patent UNITED STATES PATENTS 2,634,961 Ljungstrom Apr. 14, 1953 2,795,279 Sarapuu June 11, 1957' 2,799,641 Bell July 16, 2,801,090 Hoyer a July 30, 1957 2,818,118 Dixon Dec. 31,

Gardner Mar. 29, 1921 i 

1. A PROCESS FOR PRODUCING HYDROCARBONS FROM OIL SHALE IN SITU WHICH COMPRISES PROVIDING AN ELECTRICAL CONDUCTOR CABLE, FULLY INSULATED EXCEPT A LOWER END SECTION THEREOF AND EXTENDING FROM GROUND SURFACE INTO A LOWER LEVEL OF SAID SHALE WITHIN A BOREHOLE; PACKING SAID BOREHOLE AROUND SAID CABLE SOLELY WITHIN SAID SHALE WITH A PARTICULATE ELECTRICAL CONDUCTIVE MATERIAL IN CLOSE CONTACT WITH SAID SHALE AND IN CONTACT WITH THE LOWER UNINSULATED END OF SAID CABLE AS A FIRST ELECTRODE; PROVIDING A CASING EXTENDING INTO THE UPPER SECTION OF SAID CONDUCTIVE MATERIAL AS A SECOND ELECTRODE IN SAID SHALE; PASSING ELECTRIC CURRENT BETWEEN SAID ELECTRODES THRU SAID CONDUCTIVE MATERIAL SO AS TO HEAT ADJACENT SHALE AND RENDER SAME CONDUCTIVE AND DISTILL HYDROCARBONS THEREFROM; AND RECOVERING PRODUCED HYDROCARBONS FROM A BOREHOLE IN SAID SHALE COMMUNICATING WITH THE HEATED AREA. 